Collapsing volcanoes could produce megatsunamis hundreds of feet high

Imagine a tsunami up to 800 feet high—its size and strength ultimately submerging an island over 30 miles away.

According to researchers, the Fogo volcano swiftly collapsed and caused exactly that about 73,000 years ago.

To gauge the extent of the megatsunami, the team took stock of bizarre boulder formations on Santiago Island, 34 miles away from the Fogo volcano. Those boulders didn't comport with the geology of the island itself, but instead appeared to have been moved from the shore and placed inland. The size of the wave was determined by calculating how much energy it would have taken to move the boulders—some weighing up to 770 tons—up and over so far across the island. All this was due to what's called a "flank collapse" and such collapses could pose threats even today.

Though most scientists are skeptical of the possibility, smaller flank collapses causing tsunamis have happened multiple times over the past few hundred years.

Ricardo Ramalho, one of the lead researchers said, "Flank collapses can happen extremely fast and catastrophically, and therefore are capable of triggering giant tsunamis. We need to take this into account when we think about the hazard potential of these kinds of volcanic features."